Hydrogenation reaction is an exothermic reaction. Therefore for the multi-bed hydrogenation reactor, as the temperature increases after the oil reacts with hydrogen in the upper bed, in order to meet the requirement of carrying on the hydrogenation reaction in the next bed, the temperature of mixture has to be controlled, i.e. reducing the temperature of reactant with cool hydrogen. The reactor becomes bigger in pace with the development of hydrogenation technique. And an un-evenly heating exchanging on the radial cross section of the catalytic bed may result in an un-evenly distribution of the material temperature. For instance, the radial temperature differences at the exits in the fourth bed and in the fifth bed in certain hydrocracking apparatus before modification are up to 37° C. and 39° C., respectively. Since the radial temperature difference is too big, a hot spot takes place in the lower portion of the fifth bed, and becomes lump, which significantly shorten the life cycle of the catalyst (Petroleum Processing and Petrochemicals, 2000, 31(11): 51-54). The hydrogenation reactions are mostly under the high temperature and high pressure working conditions, thus the equipment investment and maintenances cost will be greatly increased when the input amount of cool hydrogen and the space increase. Thus, the cool hydrogen has to be sufficiently mixed with hot reactant material such that it obtains a more uniform distribution of temperature and material in the next bed. Therefore, the high efficient heat exchanging between the cool hydrogen and reactant material is the prerequisite to sufficiently carry out the performance of the catalyst and to stable operate for the apparatus.
The structure of quench box is complicated. There are usually a number of technical features in one quench box, which makes it difficult to distinguish from each other. The quench box primarily is often categorized into 3 types as follows:
(1) Flowing Around Type which means that reactant sinks to the annular space outside the mixing chamber and enters the mixing chamber through the pores on the outer wall of mixing chamber, while cool hydrogen enters the mixing chamber through the pores on the inner wall of mixing chamber and is preliminary mixed with the reactant in the mixing chamber, then the mixture further flows around the quench cooler during which a uniform distribution of material and temperature is achieved.
(2) Baffling Type which means that the reaction medium and cool hydrogen enter the quench cooler from the annular channel on the upper end of quench cooler, then are baffled and discharged from the lower end of quench cooler, during which a uniform mixing of fluid is achieved.
(3) Rotary Vane Type which means that the quench box is equipped with vane, and the fluid is rotated and mixed under the drive of the vane.
Three patents, “Quench assembly design” (U.S. Pat. No. 4,960,571), published in 1990 by Exxon Research and Engineering company, “Multiphase mixing device with improved quench injection for inducing rotational flow” (US 20040234434), published in 2004, and “Quench box for a multi-bed, mixed-phase cocurrent downflow fixed-bed reactor” (U.S. Pat. No. 7,112,312), published in 2006, all comprises both technical features of “flow around” and “baffling”. “Fluids mixing and distributing apparatus” (U.S. Pat. No. 5,403,560, U.S. Pat. No. 5,567,396) published in 1995 and 1996 by Texaco Inc., “Two phase fluid heat exchange” (U.S. Pat. No. 5,756,055) published in 1998 by UOP company and etc., are similar to above three patents. And the patent “Method and apparatus for mixing and distributing fluids in a reactor” (U.S. Pat. No. 5,462,719) proposed in 1995 by Atlantic Richfield Company has a typical rotary vane structure.
In summary, the design method of quench box described in above patents can be generalized into 2 principles: increasing retention time and baffling and impinging of the fluid in the quench box so as to achieve the purpose of fluid mixing and transferring heat. Although these methods is industrialized and brings about almost satisfying effect, there is still a problem of oversize in volume, which mainly results from that a high mixing efficient can only be achieved by combining various mixing manners. Obviously, it must start from improving the mixing manner, achieving multifunctional structure of the device, that is, combining the features of flowing-around, baffling and rotation, to develop a novel mixing device.
In order to better utilize the space volume in the reactor, Chinese Patent ZL 2006 2 0162611.7 introduce the concept of “cyclone” into the design of quench box, which converts the potential energy of the falling fluid into cyclone kinetic energy, increasing the turbulent intensity while prolonging the retention time. This patent is fundamentally different from the two-dimensional space cyclone quench box disclosed in ZL 97202630.4 and in ZL 00253961.6. Although this patent has breakthrough in concept, the oxygen absorbing efficient measured is 61.45%, which needs further improvement.
The hydraulic cyclone quench box ZL 2006 2 0162611.7 has following technical defects:
(1) The swirling intensity is insufficient. The cyclone mechanical energy of the patent totally comes from the kinetic energy of gas-liquid 2-phase fluid which flows downward from the upper bed through a downcomer, thus only a high gas-liquid flow velocity can produce enough mechanical energy.
(2) The mechanical energy of cool hydrogen is not utilized. Similar to today's most patent, cool hydrogen in this patent is also injected from the cool hydrogen pipe nozzle to the reactor. Therefore, the cool hydrogen is only served as a medium to be mixed, but not a power.
(3) The downcomer employs cylindrical pipe. In order to obtain the cyclone effect, the diameter of the downcomer is often less than ½ of the diameter of the swirl tube. In fact, the less the diameter of the swirl tube, the better the cyclone effect. Accordingly, the diameter of downcomer has to be decreased, which increases falling resistance of the gas-liquid mixing fluid.
(4) There is no mixing element provided inside the mixing chamber and at the exit of the mixing chamber. Although the downcomer is tangent to the mixing chamber, and fluid can flow into the mixing chamber in a cyclone manner, the different fluid flowing into the mixing chamber cannot be mixed because there is no mixing element provided inside the mixing chamber and at the exit of the mixing chamber.